Field devices are widely applied in automation technology for registering measured values, e.g. pressure, temperature or flow, e.g. flow rate, at process components. As a rule, the measured values are forwarded to superordinated units, e.g. control units or systems, where they can be further processed or displayed.
Besides a data transmission from the field device to a receiver, also a data transmission to the field device is necessary, e.g. for the setting of configuration or parametering data. Via correspondingly selected parameters (units of measurement, limit values, etc.), field devices can, thus, be adapted to the particular measurement task.
Data transmission between field devices and superordinated units occurs, mostly, via fieldbus systems (Hart, Profibus or Foundation Fieldbus) with corresponding cable connections. If the energy (or power) supply occurs via the fieldbus, then one speaks of bus-fed, or 2-wire devices. If, besides the fieldbus, an additional connecting line is necessary for the energy supply, then one speaks of 4-wire devices.
For some time, also cable-less networks, so-called radio networks, have become known for sensors. Such a radio network is described in more detail in U.S. Pat. No. 6,208,247.
In the case of the sensors of this radio network, however, only a data transmission in one direction is possible, and, indeed, from the sensor to the superordinated unit. I.e., only the pure, measured values can be transmitted to the superordinated unit. This excludes the possibility of configuring or parametering field devices from the control system. Radio networks are suited especially for those industrial applications where no cabling is desired, or where cabling is only possible at great expense.
Radio networks for sensors are already specified in some detail in the standard, IEEE 802.15.4. An industry consortium, the ZigBee Alliance, is now developing application profiles, network- and security-standards for various areas of application using this new technology.
Developing sensors (field devices) for radio networks is very complex and expensive.